The present disclosure is directed to the field of Wireless Local Area Networks (WLAN's), with particular applicability to switching devices used with wireless access points in a WLAN. In a WLAN, 10 as shown in FIG. 1, a number of clients 12, e.g., laptop computers, etc., include a wireless card 14 for enabling mobile radio communication with an access point (AP) 16. Each AP 16 has a radio card 18 for communicating with mobile clients 12. The AP 16 communicates with mobile clients in accordance with the IEEE 802.11 protocol. The AP 16 can use a single radio card 18a or also a second card 18(b) to allow transmission in the 2.4 GHz band in accordance with the IEEE 802.11(b) and (g) standards, or in the 5 GHz band in accordance with the IEEE 802.11(a) standard. The AP 16 can also use more than two radios if desired.
The AP 16 is connected to an Ethernet cable 20, which in turn connects to a network switch 22, from which mobile client communications are sent out onto the network 10. The Ethernet cable 20 carries signals in accordance with the IEEE 802.3 protocols (10, 100, 1000 Base-T). For data frames or packets exchanged between mobile clients 12 and the network 10, a basic function of the AP 16 is to provide a back-and-forth conversion between the 802.11 and 802.3 protocols; either 802.3 to 802.11 translation downstream and 802.11 to 802.3 translation upstream or 802.11 encapsulation of the 802.3 packets.
As shown in FIG. 2, the network switch 22 has a number of ports 24 for enabling a number of APs 16 and other network devices to connect to the LAN 10. In a large enterprise rollout, a switch 22 can typically have 12-48 ports. In order to route packets between the network 10 and the client devices, the switch 22 includes a switch chip 26. The switch chip 26 is an ASIC (Application-Specific Integrated Circuit). The switch ASIC 26 also cooperates with a central processing unit (CPU) 28, which helps configure the switch ASIC 26. The CPU 28 and the switch ASIC 26 are typically connected over a PCI bus or a MII bus. This allows a memory mapping of the switch chip internal buffers, allowing the CPU access to the buffers when it is required. Similarly, if the switch chip cannot automatically forward a packet, then it will be buffered, allowing the CPU to forward the packet manually. The switch 28 also includes an uplink 30 to connect the switch back to the WAN 10.
In previous-type systems, a typical network switch 22 encounters performance-related problems when used with wireless components. A typical switch ASIC 26 does not have the capability to distinguish between wireless data traffic and any other ordinary network data traffic. An ASIC is a hard-coded “state machine,” in which the functions are hard coded and built using AND gates, OR gates, and flip-flops and is fixed directly in the silicon. A typical switch ASIC 26 can only switch packets to the ports 24. But since the AP 16 itself can handle 10-15 clients, network bandwidth can bog down between the AP 16 and the switch 22, since the wireless clients share a single switch port 24, for reasons, which will be explicated below. One of the principle functions of an Access Point 16 is to receive frames encoded in the 802.11 wireless format and transforms the frames into the 802.3 ethernet format, and visa-versa.
Depending on the configuration, the AP will translate the packets from 802.3 to 802.11 downstream (toward the AP), and translate from 802.11 to 802.3 upstream or fully encapsulate the 802.3 packet in an 802.11 packet. Each frame has a header with other into such as a start frame delimiter, a source address, etc., each with a certain number of bits in a certain order defined by the respective IEEE 802 protocol. The middle of each frame includes data, and the end of a frame includes a CRC check (error check). The 802.11 frames are very similar to the 802.3 frames, but include information with specifics of the wireless radio transmission properties. A typical AP includes other functionality, such as security functions for associating new users to the network, and performing filtering so as to limit network access for certain users already associated. It should also be noted that a certain amount of the 802.11 protocol must be done at the 802.11 MAC. This includes inserting the packet sequence numbers for the next packet that the MAC will attempt transmission on. Due to the uncertain nature of packet transmission in the wireless network, the 802.11 protocol is robust against packet transmission errors. But because of the 802.11 MAC must manage the ordering of the transmitted packets directly and be able to select the next packet from the various queues (i.e., QoS, Power Save Data).
In a typical LAN, a lot of data traffic is coming up and down the uplink 28 to the switch 22. This traffic includes unicast, multicast and broadcast frames. No problems are encountered with unicast traffic, since packets are intended for a particular recipient, and the switch ASIC 26 directs the packets across the specific intended port 24. However, problems are encountered when sending multicast and broadcast packets, since they are sent to multiple recipients or all recipients. These types of packets go to all the ports 24 of the switch 22. Since such multicast and broadcast traffic is not intended for the wireless clients 12, the AP 16 can get bogged down fending off this traffic.
The typical previous-type switch ASIC also presents other problems. Some types of network traffic have higher bandwidth considerations than other types. For example, in a phone conversation (when using a VoIP 802.11 based phone), a certain amount of data must move more quickly than e.g., web browsing. For this reason, “Quality of Service” (QoS) considerations are established to give higher priority to packets that make up the time bound data traffic. Standards of QoS are specified in the Ethernet and wireless protocols, IEEE 802.3(g) and 802.11(i), respectively.
Another primary difference between a wireless switch and a standard switch is that some wireless clients are in a power save mode. When a wireless client is in a power save mode it cannot immediately accept data. In power save mode, a wireless client can only accept data after it wakes up and responds to the power save poll that occurs as part of the 802.11 Beacon process.
This power save function forces the wireless switch to include a store and forward mechanism as part of it's normal operation. Thus, a wireless switch must not only process time bound QoS packets, but also time delayed power save packets. Similar in that both kinds of traffic require their own queue management, but different in the manner in which the queues are managed.
Examples of this power save mechanism are many. One application is where all of the wireless clients are low power handheld computing devices that would always be in power save mode due to limited battery runtime. Another example of a power save wireless client is an 802.11 VoIP phone waiting for a call. The phone would be in power save mode until it “Rang”, and was answered.
VLANs help IT managers configure and segment a network. A “virtual LAN” (VLAN) is a group of wireless clients, wired computers, servers, and other network components that function as if they were connected to a single network segment even though they are not. A VLAN enables particular users and resources to be grouped in a logical manner, regardless of the network segment(s) to which they may be physically connected. For example, a VLAN may be used to define a group of visitors to allow wireless internet access but deny access to secure network resources. However, a typical switch ASIC 28 is not capable of distinguishing 802.11 wireless packets for QoS and VLAN purposes.